This invention relates to touch-operated switching devices. More specifically, this invention relates to rectangular arrays of pressure sensitive switching elements that are relatively transparent and thus permit various alphanumeric characters or other symbols to be viewed through the switching array.
The type of switching array addressed by the present invention includes a relatively pliant or flexible planar sheet of material that is spaced apart from and parallel to a relatively rigid planar backplate of substantially identical curvature. To define a desired array of n rows and m columns of switching elements, the surface of the backplate that faces the pliant sheet material includes n parallel strips of conductive material and the juxtaposed surface of the pliant sheet includes m conductive strips that are parallel to one another and perpendicular to the conductive strips of the backplate. With this configuration, the application of pressure that sufficiently deforms or flexes the pliant sheet toward the backplate will cause one of the conductive strips on the pliant sheet to contact one of the conductive strips on the backplate. Since the parallel spaced conductors of the backplate and pliant sheet can be considered to correspond to the rows and columns of the rectangular switching matrix and are easily defined in terms of an orthogonal rectangular coordinate system (Cartesian coordinate system), switching devices of this type are sometimes referred to as X-Y switching arrays or X-Y selectors.
Prior art X-Y selectors and other arrays of touch-operated switches often serve as a keyboard for use with a wide variety of electrical and electronic systems wherein human control or interaction is necessary. In this regard, there are a growing number of situations in which it is either desired or necessary to change the function or operation defined by one or more keys within such a switching array during a particular sequence of keyboard operations or to change functions of the keys so that a completely different operational sequence can be implemented. For example, such a keyboard can be used advantageously in a programmed electronic instrument or system wherein operator interaction is required to sequence the system or instrument through a series of various computational steps or other operations that may vary, depending on the keys selected by the operator and/or the results of the previous step of the sequence.
In many instruments and systems of the above-described type, the number of switching elements required during each step of an operational sequence often varies and it may be desirable to utilize a different keyboard pattern or configuration at different steps of the sequence. In addition, to minimize the training and level of skill necessary to operate such an instrument or system, it is often desirable to visually present instructions or other information to the operator at each step of the sequence that requires operation of one or more keys.
One prior art proposal for permitting various instructions and comments to be displayed within an associated set of keys or switches that are defined in accordance with the operational step or sequence being performed utilizes an X-Y selector of the above-described type that is mounted to the face of a cathode-ray tube (CRT) or a similar display device with the pliant sheet, the backplate and the conductive strips all being formed of a transparent material. Since numerous techniques are known for generating virtually any desired symbol or character with either raster scan systems (such as conventional television) or X-Y deflectable electron gun systems (such as conventional oscilloscopes) and since most systems or instruments that include computational or programming capability can store the information required to generate a relatively large number of various displays, such an arrangement offers considerable advantages.
Prior to this invention transparent switch arrays have not proven totally satisfactory in the above-discussed arrangements and have exhibited one or more distinct disadvantages or drawbacks. For example, in one prior art device a relatively thick rectangular frame that borders the viewing area of the associated cathode-ray tube is used to separate a relatively thin, transparent sheet that includes several columns of conductive material from a rigid transparent backplate that includes several rows of conductive material. Even with the frame member providing a substantial separation between the transparent sheet and the backplate, sag or stretching of the transparent sheet sometimes occurs to the extent that conductive row and column elements come into contact with one another without being intentionally activated. Moreover, when the separation or gap between the adjacent conductive row and column elements is minimized so as to provide as large a number of switches as possible, such prior art devices often permit more than one conductive row and column element to come into contact so that ambiguous or false switching signals are generated. Both of these problems generally increase with switch usage and can be affected by environmental conditions such as temperature and humidity. Thus, equipment using such a transparent switch array often has generated a considerable number of field complaints and the switch arrays generally have had a relatively short service life.
Another factor that has contributed to the relatively short lifetime of most prior art transparennt switch arrays and also has resulted in various other disadvantages and drawbacks is the structural complexity of such devices. For example, in the above-mentioned prior art device which employs a rectangular frame for spacing the conductive elements apart from one another, electrical connection to each conductive column and row is provided by metal eyelets that are installed in the terminal region of the conductive strips with wires being inserted into and soldered to the eyelets. Because of space limitations, each wire that connects to a conductive strip of the pliant member must pass through an individual hole in the border region of the rigid backplate. Thus, considerable time is required to fabricate the various components and assemble such a device. Moreover, because at least the soldered connections to the pliant member must be removed before such a switching array can be disassembled, it is generally not practical to attempt to repair such a prior art device by, for example, replacing the pliant member.
In addition to the above-discussed problems, prior art devices have not always allowed the characters generated on the cathode-ray tube to be observed as readily as is desired. For example, to provide good viewing characteristics, the switching array must not diffuse or distort the characters produced on the cathode-ray tube. Further, to permit the display generated by the cathode-ray tube to define different switching formats that use a selected number of the arrayed switches at selected positions within the rectangular matrix that forms the switch array, the separation between the rows and columns (and hence between the switching elements) should be as visibly indiscernible as possible. Although materials of sufficient transparency are available, the visual or optical properties of prior art devices have not been completely satisfactory. For example, in prior art devices wherein the pliant member is spaced apart from the backplate by a fairly substantial distance, some distortion of the characters generated by the cathode-ray tube occurs and parallax may be a problem. Moreover, in many situations the equipment employing the switch array and cathode-ray display is operated under relatively high ambient lighting conditions wherein observation of the displayed characters or symbols becomes somewhat difficult. In such situations, various optical properties of prior art switch arrays such as lack of a high transmissibility at the wavelength of the luminescent display and high reflectivity of the pliant sheet material has caused additional degradation in the quality of the display.
Accordingly, it is an object of this invention to provide a relatively transparent switch array that can be utilized in conjunction with a cathode-ray tube or other type of display device to generate various switching formats and configurations.
It is another object of this invention to provide a transparent switch array wherein the backplate and the pliant member are closely spaced so that the assembled switch array is relatively thin and exhibits good optical properties.
It is still another object of this invention to provide a relatively transparent switch array that exhibits improved viewing of luminescent displays under various ambient lighting conditions relative to the quality of such displays in the absence of the switch array.
Even further, it is an object of this invention to provide a transparent switch array of the above-described type that is relatively simple to fabricate and repair to thereby provide a device that can be manufactured and maintained at a reasonable price.